1. Field of the Invention
The invention relates to a process and apparatus for mixing gases in a specified proportion and dosing the resultant gas mixture to a point of use and somewhat more particularly the invention relates to a method and apparatus for precisely mixing various gases and transmitting known amounts thereof for anesthesiological and respirational treatments.
2. Prior Art
A known method of mixing gases for anesthesiological and/or respirational treatments utilizes mechanical systems which contain differential pressure regulators and throttle/valve arrangements. Such mechanical systems do not allow any greater precision than about .+-.3% and function only in a limited gas pressure flow range. Further, the function of such a system is unreliable in instances of low gas pressure. In order to obtain a satisfactory precision where small mixed gas streams are required, in certain instances, a larger gas stream must be transmitted through a mixer whereby a large portion of the provided gas quantity cannot be utilized. Yet further, a mechanical system of this type is not reliable because its function can be interfered with by dirt or the like reaching operational elements of the system. Through a functional interference of this type, the gas sources which are connected with such a mechanical system, can come into direct communication with one another so that gas can flow from one gas source with a higher pressure into another gas source with a lower pressure, particularly if the gas mixture is not removed from the mixing system. The results can entail catastrophic consequences; for example, when laughing gas (N.sub.2 O) and oxygen gas, which are both odorless, are being mixed, they can mistakenly be readily interchanged. Further, the dosing of the resultant gas mixture must be conducted with a specific apparatus that is not a component part of the mixing system; for example, with a rotary meter having an adjustable throttle or choking valve positioned after the mixing system.
Another known method of mixing and dosing gases comprises directly mixing a plurality of gases with the aid of individual rotary meters for each gas with series-connected adjustable throttles. In practice, with this type of an arrangement, precision of no more than about .+-.10% can be obtained. In order to obtain a gas mixture having a desired proportion of individual gases therein, the necessary flow for each gas must be precalculated and individually adjusted.
In anesthesia a desirable requirement is being able to record the concentration of the various gases in a gas mixture being utilized and being able to record the flow of this gas mixture. Further, another desirable requirement is for an alarm means which indicates when the composition of a gas mixture or when the volume of the gas stream does not agree with an adjusted (predetermined) value. These requirements cannot be satisfied with the systems that are based on the two above discussed methods; on the contrary, such requirements can only be satisfied by providing expensive electronic measuring devices.